1. Field of the Invention
This invention relates generally to motorized riding trowels for finishing concrete surfaces, and to steering and blade pitch control systems therefor. More particularly, the present invention relates to control systems for self-propelled riding trowels, and to trowels equipped with such systems. Representative prior art self-propelled riding trowels are classified in United States Patent Class 404, Subclass 112.
2. Description of the Prior Art
Self-propelled, motorized riding trowels have become widely accepted in the concrete finishing arts. High-power, multiple engine riding trowels are particularly effective. They can finish large surface areas of wet concrete much more efficiently than single engine riding trowels or the older "walk behind" trowels. Significant savings are experienced by the contractor using such equipment, as time constraints and labor expenses are reduced.
Typical motorized riding trowels employ multiple, downwardly projecting rotors. The rotors contact the concrete surface for finishing concrete and support the weight of the trowel. Typically each rotor comprises a plurality of radially spaced apart finishing blades that revolve in frictional contact with the concrete surface. The blades may be coupled to circular finishing pans for treating green concrete. The rotors and their revolving blades are responsible for steering and propulsion. To effectuate steering the rotors are tilted to generate differential forces.
Generally speaking, the more powerful the trowel, the faster finishing operations can be completed. However, the more powerful the trowel, the more difficult it can become to steer the machine. Crisp, responsive handling is important to optimize the efficiency of the troweling process, and to preserve operator safety and comfort.
Holz, in U.S. Pat. No. 3,936,212 describes a three-rotor trowel powered by a single engine. Devices of this nature are difficult to steer, in part because the manually-operated steering linkages that are conventionally employed are inefficient and cumbersome. Further, the drive motor linkages are unreliable and inordinately complex. In U.S. Pat. No. 4,046,484 Holz discloses a twin rotor trowel that is the forefather of many twin rotor designs presently on the market. Trowel steering and propulsion is effectuated by the combination of rotor tilting and blade twisting. Both prior art Holz devices are powered by a single motor. The rotors are driven by an engine mounted on the frame. By tilting the axis of rotation of the rotors, steering and directional control are varied. Frictional forces developed as the blades (or pans) revolve upon the concrete surface resolve into propulsion forces that move the trowel.
Notwithstanding their advantages over older manual systems, early riding trowels based upon the original Holz design were cumbersome and difficult to control. For steering the rotors were tilted with manually operated lever arrangements that projected upwardly from the machine frame. The operator was required to manually control the levers, and a vigorous physical effort was required. The steering characteristics of the trowel disclosed in U.S. Pat. No. 5,108,220, which is owned by the same assignee as in this case, are enhanced. The latter reference discloses a fast steering, high power, twin rotor riding trowel that substantially enhances maneuverability and control over prior twin-rotor machines. Physical labor of the driver is reduced, as the improved linkages and offset couplings therein reduced the effort required to tilt the rotors. However, the driver is nevertheless required to manually deflect levers to steer and control the device.
Significant riding-trowel power is required if large areas of concrete are to be trowelled in a short period of time. U.S. Pat. No. 5,480,258, which is owned by the same assignee as in this case, discloses a multiple engine riding trowel. The twin rotor design depicted therein associates a separate engine with each rotor. As the engines are disposed directly over each revolving rotor assembly, horsepower is more efficiently transferred to the revolving blades. Besides resulting in a faster and more efficient trowel, the design is easier to steer. Again, manually activated steering linkages are used.
Twin-rotor trowels can have "overlap" problems. When the rotors are spaced apart from one another for clearance purposes, an unfinished region between the revolving blades results. To remedy the overlap problem, earlier twin rotor riding trowels meshed their rotor blades to avoid these unfinished intermediate areas. Such designs require synchronization of the propeller-like rotor blades to avoid destructive interference. This timing problem complicates transmission design, especially in single engine riding trowels. In multiple engine designs meshed rotors necessitate properly synchronized motors.
Prior approaches at motor synchronization have been difficult electronically and dangerous mechanically. Another consideration mitigating against the use of meshed rotor trowels is that such designs cannot easily handle finishing pans. Such pans are used to treat green or wet concrete during early stages of the finishing process. They are attached to rotors by seating the rotor blades within suitable brackets. However, they generally cannot be used on trowels where rotor spacing meshes the blades, as adjacent pans collide. To fit pans the rotor spacing must be increased. However, in twin rotor machines if the rotor spacing is increased to accommodate pans, the gap between adjacent rotor blades increases.
Systems that have more than two rotors easily "cover" the intermediate surface area between adjacent rotors, thus avoiding the overlap problem. Coverage results whether the trowel is running blades or finishing pans. Significantly, there is no rotor synchronization requirement in a three or four rotor trowel, as the blades need not be meshed to avoid the overlap problem. However, as rotors are added, drive horsepower must be increased. Steering linkage complexity is aggravated as multiple rotors are added. Further, where separate engines are used with each rotor assembly, more and more physical effort is required to manually tilt the rotors for steering, or to vary blade pitch.